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Fix crash on partially typed namespace package #20742

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Fix crash on partially typed namespace package #20742

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1eb8081
Fix crash on partially typed namespace package
ilevkivskyi Feb 4, 2026
d251576
Typo
ilevkivskyi Feb 5, 2026
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20 changes: 12 additions & 8 deletions mypy/build.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3144,9 +3144,9 @@ def find_module_and_diagnose(
raise ModuleNotFound
if is_silent_import_module(manager, result) and not root_source:
follow_imports = "silent"
return (result, follow_imports)
return result, follow_imports
else:
# Could not find a module. Typically the reason is a
# Could not find a module. Typically, the reason is a
# misspelled module name, missing stub, module not in
# search path or the module has not been installed.

Expand All @@ -3155,7 +3155,7 @@ def find_module_and_diagnose(
# Don't honor a global (not per-module) ignore_missing_imports
# setting for modules that used to have bundled stubs, as
# otherwise updating mypy can silently result in new false
# negatives. (Unless there are stubs but they are incomplete.)
# negatives. (Unless there are stubs, but they are incomplete.)
global_ignore_missing_imports = manager.options.ignore_missing_imports
if (
is_module_from_legacy_bundled_package(id)
Expand Down Expand Up @@ -3650,7 +3650,7 @@ def load_graph(
added = [dep for dep in st.suppressed if find_module_simple(dep, manager)]
else:
# During initial loading we don't care about newly added modules,
# they will be taken care of during fine grained update. See also
# they will be taken care of during fine-grained update. See also
# comment about this in `State.__init__()`.
added = []
for dep in st.ancestors + dependencies + st.suppressed:
Expand Down Expand Up @@ -3710,11 +3710,15 @@ def load_graph(
assert newst.id not in graph, newst.id
graph[newst.id] = newst
new.append(newst)
if dep in graph and dep in st.suppressed_set:
# Previously suppressed file is now visible
# There are two things we need to do after the initial load loop. One is up-suppress
# modules that are back in graph. We need to do this after the loop to cover an edge
# case where a namespace package ancestor is shared by a typed and an untyped package.
for st in graph.values():
for dep in st.suppressed:
if dep in graph:
st.add_dependency(dep)
# In the loop above we skip indirect dependencies, so to make indirect dependencies behave
# more consistently with regular ones, we suppress them manually here (when needed).
# Second, in the initial loop we skip indirect dependencies, so to make indirect dependencies
# behave more consistently with regular ones, we suppress them manually here (when needed).
for st in graph.values():
indirect = [dep for dep in st.dependencies if st.priorities.get(dep) == PRI_INDIRECT]
for dep in indirect:
Expand Down
2 changes: 1 addition & 1 deletion mypy/modulefinder.py
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Original file line number Diff line number Diff line change
Expand Up @@ -471,7 +471,7 @@ def _find_module(self, id: str, use_typeshed: bool) -> tuple[ModuleSearchResult,
if fscache.isdir(path):
if fscache.isfile(stub_typed_file):
# Stub packages can have a py.typed file, which must include
# 'partial\n' to make the package partial
# 'partial\n' to make the package partial.
# Partial here means that mypy should look at the runtime
# package if installed.
if fscache.read(stub_typed_file).decode().strip() == "partial":
Expand Down
18 changes: 18 additions & 0 deletions test-data/unit/pep561.test
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Expand Up @@ -233,3 +233,21 @@ our/bar.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#
[out2]
our/bar.py:1: error: Skipping analyzing "typedpkg_ns.b": module is installed, but missing library stubs or py.typed marker
our/bar.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports

[case testPartiallyTypedNamespacePackageNoCrash]
# pkgs: typedpkg_ns_nested
import a
[file a.py]
import m1
import m2
[file a.py.2]
import m1
[file m1.py]
import typedpkg_ns.b # type: ignore
[file m2.py]
import typedpkg_ns.a
# TODO: the error on second run is a bug, but it is a separate issue, likely #20105.
[out]
[out2]
m1.py:1: error: Skipping analyzing "typedpkg_ns": module is installed, but missing library stubs or py.typed marker
m1.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports